1. Field
The disclosure relates to a method, system, and article of manufacture for the management of point-in-time copy relationship for space efficient volumes.
2. Background
A storage controller may control a plurality of storage devices that may include hard disks, tapes, etc. A cache may also be maintained by the storage controller, where the cache may comprise a high speed storage that is accessible more quickly in comparison to certain other storage devices, such as, hard disks, tapes, etc. However, the total amount of storage capacity of the cache may be relatively smaller in comparison to the storage capacity of certain other storage devices, such as, hard disks, tapes, etc., that are controlled by the storage controller.
The storage controller may perform point-in-time copy operations to copy source storage volumes to target storage volumes, where a point-in-time copy is a fully usable copy of a defined collection of data that contains an image of the data as it appeared at a single point in time. The copy is considered to have logically occurred at that point in time and the data in the target storage volumes is a consistent copy of the data as it appeared at that point in time in the source storage volumes. FlashCopy* is a point-in-time copy mechanism implemented by International Business Machines Corporation. *FlashCopy is a trademark or registered trademark of International Business Machines Corporation.
A space efficient volume is a type of storage volume that does not occupy physical capacity when it is created. Space gets allocated when data is actually written to the space efficient volume. In other words, space for a space efficient volume is allocated when a write occurs, and more precisely, when a destage from the cache occurs and there is no allocated space designated for the write on the currently allocated extent or track.